The chairman and the general secretary of the embattled Police Federation will both retire at the end of next month, the organisation announced today.

Following the Plebgate row and an independent review that revealed millions of pounds held in unaccounted reserves, chairman Steve Williams and general secretary Ian Rennie have both decided to leave the police service and their roles in the Federation.

Mr Williams said: "The Police Federation has faced a turbulent period in its history and there has been much criticism of our organisation and the way certain members behaved.

"When I took up office it was quite clear that as an organisation we were not fit for purpose and that is why I, along with my joint central committee colleagues, commissioned an independent review to help us identify our weaknesses and come up with solutions of how we could do things differently.

"When the independent review was published in January, it delivered a hard-hitting report that clearly showed that we were not delivering what our members wanted, were failing in key areas and that many of our practices were outdated. But it gave the leadership of the organisation a clear mandate, with 91% of the membership surveyed indicating that they wanted change.

"Over the last few months, despite at times some significant challenges and opposition along the way, I have tried to manoeuvre the organisation to a place whereby we can start to deliver what is best for the Police Federation, its members and the British police service as a whole.

"Having reflected on where we now are, I feel that it is only right and proper that PFEW (the Police Federation of England and Wales) elects a new chairman to take this organisation into the next phase."

Mr Williams and Mr Rennie will leave in late May, after the Police Federation's annual conference.

Mr Williams said: " The federation has a vital and important role to play in policing, but I have made no secret of my fears that unless we get this right and embrace the change required others will do it to us, a view echoed recently by the policing minister, Damian Green.

"I have had over 30 wonderful years in policing and during that time I have had the privilege of working with some great people.

"It is in the interest of all those involved in policing that we build a federation that represents the best interests of the brave men and women who police our communities, villages and towns and that we develop an organisation that we can once again say is the voice of policing. That will be the best prize of all."

A review of the Police Federation by charity the RSA published in January found that the body had around £95 million in reserves and assets.

The organisation was deeply divided into local factions, most of which refused to share details of their accounts with the investigators.

Researchers found there were centrally held reserves of £29.5 million and those held by branch boards stood at around £35 million, but there was also another estimated £30 million in separate accounts, details of which were not given to the national heads of the organisation.

The RSA said that subscription rates should be cut by 25% in 2015, subsidised by central reserves, in a bid to hand back some of the money to members.

The federation represents officers from the rank of constable to inspector, and has around 127,000 members in England and Wales.

It became embroiled in the so-called Plebgate row after then-chief whip Andrew Mitchell had a foul-mouthed confrontation with an officer guarding Downing Street in September 2012.

Mr Mitchell, who was accused of calling the officer a ''pleb'', which he denied, was forced to resign his post following a month of intense media interest in the story.

The saga continued the following month when members of the Warwickshire, West Mercia and West Midlands branches met with the politician in his Sutton Coldfield constituency in a bid to clear the air.

Detective Sergeant Stuart Hinton, Inspector Ken MacKaill and Sergeant Chris Jones claimed that he had refused to reveal what he had actually said, but this was apparently contradicted by a secret recording of the meeting.

They were later hauled before MPs to explain what had happened.

Chairman of the Home Affairs Select Committee Keith Vaz said: "I am amazed and surprised by the proposed retirement of two people who have been instrumental in instigating reform in the Police Federation.

"Although evidence given to the Home Affairs Select Committee so far has shown examples of bullying and inappropriate behaviour, I assumed that the leadership of the federation was united in seeking fundamental reform.

"These retirements will leave this important organisation with a huge vacuum and leaderless at a time when they need strong direction. It will remain to be seen if the federation will continue on the path of change.

"We will be seeking answers from Sir David Normington, Martyn Mordecai, the treasurer of the federation, and the Home Secretary when they appear before us tomorrow."

Home Secretary Theresa May said: "As chairman, Steve Williams understood that the Police Federation needs to change, and I am sorry that he will be retiring in May.

"Steve has chaired the Federation through a difficult time for policing in England and Wales. He was right to commission the Normington Review, which recommended radical and urgent reform to the Federation.

"If the Federation is to have public legitimacy, the Normington recommendations now need to be implemented, in full and in good time."I wish Steve the best of luck for the future."

College of Policing chief executive Chief Constable Alex Marshall said: "Both Steve Williams and Ian Rennie have worked tirelessly to ensure the voice of the Federated ranks are reflected at the national level.

"They have been the drivers of reform at the Federation and have shown a determination to move the organisation into a new era.

"Both Ian and Steve have worked closely with the College of Policing as we continue to develop our role as the professional body for policing and I wish them the very best for the future.

"We look forward to working as constructively with their successors to help implement the changes recommended in the Normington Review to ensure that we deliver the best for Federated ranks in policing."

Sir Hugh Orde, president of the Association of Chief Police Officers, said: " Since his appointment as chairman in 2012, Steve Williams has shown great determination to modernise the Police Federation so the organisation can effectively represent rank-and-file officers.

"The independent review of the federation, commissioned by Steve, was a vital part of that process and his leadership brought the organisation into a place where it has a critical opportunity to make the necessary changes.

"At a time when reform is so important, the loss of both Steve and Ian Rennie's leadership is a great shame. Both have been passionate about ensuring that the voice of rank-and-file police officers is heard, as it must be.